1. Field of the Invention
The invention relates to a medical examination table that can be used essentially in the field of radiology. It is possible, however, to conceive of its use in other fields of medicine, for example in nuclear medicine or in the field of ultrasonics. The particular feature of radiological medical tables is that they can be used to orient the patient in space in various ways while at the same time also providing for various functions such as those relating to myelography, tomography, cardiography, angiography, etc.
2. Description of the Prior Art
A medical examination table normally comprises a pedestal laid on or fixed to the ground and an underframe holding a patient-bearing plate. The underframe can be shifted in relation to the pedestal, and the patient-bearing plate can be moved translationally in relation to the underframe. The movements of the underframe may enable, firstly, elevation so that it can receive patients in the low position when they lie on the patient-bearing plate and then raise them so that these patients are presented in a more ergonomic way to the practitioner who is supposed to work on them during the radiological examination.
Furthermore, the underframe should also be capable of tilting, notably in myelography. While the patient is strapped to the plate, the underframe should be capable of taking vertical positions with the patient's feet below and his head up, or a reverse vertical position, also called a Trendelenbourg position, in which the patient's head is pointed downwards. The motions of the patient-bearing plate in relation to the underframe are normally motions of longitudinal and lateral translation, so that certain parts of the patient's body are presented to irradiation by X-rays when the picture is taken or the radiological study is made.
Traditionally, there are two known classes of tables given the diversity of the functions to be carried out. A first class relates to the tables that can be used in tomography, as well as in general radiology. These tables essentially comprise, from the viewpoint of the invention, the function of elevation as well as, accessorily to the present problem, a possibility of angular orientation of the X-ray beam in relation to the patient. This angular orientation corresponds to the needs manifested in tomography. In practice, with the tables of this class, the patient always reclines horizontally on the patient-bearing plate. He does not, for example, ever have to be strapped to it.
The other class of tables relates to tables that can be used inter alia for the myelographic function. Essentially, their underframe tilts in both directions. In practice, for this type of tilting table, there are three philosophies. In one case, before the underframe is made to tilt in one direction or in the other, it is raised in such a way that the ends of the underframe do not strike the ground at the instant of tilting. In the second case, the tilting motion is coupled to a motion of longitudinal shift of the underframe, so as to prevent the same problem. Naturally, in both cases, there are electronic safety circuits designed to prevent any positive action that would result in such a collision. In the first and second cases, the tilting is symmetrical: +90.degree./-90.degree..
In the third case, the tilting of the underframe is dissymmetrical, i.e. 90.degree. vertically and 15.degree. to 20.degree. in the Trendelenbourg position, but it is achieved by a single mechanism. The myelographic examination is ruled out in this use but this type of underframe covers the majority of applications at a favorable cost of equipment. There is no elevation for this type of table.
The problem to be resolved by the manufacturer of such tables is that of low-cost series production. It is known, for example, that for the manufacture of these tables, the factories may be laid out as follows. Assembling stations fitted out with specialized equipment are ideally located in the factory. As and when they are completed, the tables are gradually brought closer to each of these work stations. If three type of tables are manufactured, it is necessary to plan for a threefold organization in terms of work stations and specialized equipment. This is cumbersome to manage and is also costly, and the specialized machines are themselves costly. It is therefore seen to be necessary to make tables of a single type which, depending on the equipment with which they are provided, are capable of fulfilling one function or another or even several functions.
Indeed, in applications of standard radiology and tomography, the underframe is normally borne by a vertical, motor-driven type of lift mechanism, the patient-bearing plate being motor-driven in lateral and longitudinal translation on the underframe. By contrast, for applications where the tilting is required, the underframe is fixedly joined to a circle sector element with a shape substantially identical to that of a semicircle. The rim of this circle sector element is provided with a rack with which there is engaged a toothed wheel fixed to the end of a motor shaft. When the motor runs, the circle sector rotates on itself in moving past the shaft. It then drives the tilting of the underframe vertically in one direction or another. This approach using a circle sector, which may be replaced by systems using synchronous belts or chains, is incompatible with the making of a lift mechanism, except at the cost of bulky and very complex machinery. The result thereof is that the classes of tables are completely different from one another.
A table of a tilting type that can be used for examinations in the non-horizontal position, as in patent No. GB-A-2 026 206. Similarly, other examples of such tables can be seen in the French patent applications Nos. 2 224 963 and 2 542 604. In every case, it is seen that the addition of a lift mechanism to the sector would lead to a very complicated mechanical approach.